2,3,3,3-Tetrafluoropropene is known for its properties of refrigerant and heat-exchange fluid. The process for the manufacture of 2,3,3,3-tetrafluoropropene from 1,2,3,3,3-pentafluoropropene comprises a stage of hydrogenation of 1,2,3,3,3-pentafluoropropene.
The document by Knunyants et al., Journal of the USSR Academy of Sciences, Chemistry Department, “Reactions of fluoro-olefins”, Report 13, “Catalytic hydrogenation of perfluoro-olefins”, 1960, describes the hydrogenation of 1,2,3,3,3-pentafluoropropene (HFO-1225ye) at ambient temperature over a palladium catalyst supported on alumina to give a mixture of 1,1,1,2,3-pentafluoropropane (HFC-245eb) and 1,1,1,2-tetrafluoropropane (HFC-254eb). 1,1,1,2-Tetrafluoropropane is produced in a significant amount (that is to say, approximately 50% with respect to the 1,1,1,2,3-pentafluoropropane).
The document WO 2008/030440 describes a method for the preparation of 2,3,3,3-tetrafluoropropene comprising at least one hydrogenation stage during which 1,2,3,3,3-pentafluoropropene is brought into contact with hydrogen in the presence of a catalyst. According to this document, the hydrogenation catalyst which may be suitable comprises a metal from Group VIII or rhenium and the metal can be supported.
Example 1 of the document WO 2008/030440 describes the hydrogenation reaction of 1,2,3,3,3-pentafluoropropene at 85° C. in the presence of a catalyst comprising 0.5% by weight of palladium supported on charcoal to give a stream comprising 92% of HFC-245eb and 8% of HFC-254eb.
The tests of the abovementioned prior art were carried out on the laboratory scale and the documents are completely silent with regard to the lifetime of these catalysts.
The hydrogenation reactions as described above are highly exothermic reactions and present problems on the industrial scale. In addition, a not insignificant amount of byproduct (HFC-254eb) is formed, due probably to the successive hydrogenolysis reaction of the HFC-245eb (that is to say, the replacement of a fluorine atom of the desired product by a hydrogen atom with formation of hydrofluoric acid).
The presence of a compound other than the reactants in the reaction stream can also be the cause of a rapid deactivation of the catalyst.
Furthermore, the document EP 1 916 232 provides a multistage hydrogenation reaction of an olefinic compound in order to obtain a high conversion and a high selectivity. Example 2 describes the hydrogenation in stages of 1,2,3,3,3-pentafluoropropene in the presence of a palladium catalyst supported on charcoal in four reactors with an outlet temperature of the first reactor of 99° C., an outlet temperature of the second reactor of 95° C., for a conversion of 54%, a temperature at the outlet of the third reactor of 173° C. and a temperature at the outlet of the fourth reactor of 104° C. Provision is made for cooling stages between the reactors with a temperature of the first bath of 59° C. and a temperature of the second bath of 116° C.
The process as described in the document EP 1 916 232 is expensive and, in addition, it is not easy to carry out.